This invention relates to xerographic development and, more particularly, multi-component developer materials.
In electrophotographic processes, there are a number of well known methods of developing the electrostatic image which is created on the photoconductor drum. These include cascade development, powder cloud development and magnetic brush development. All of these systems have as an object to transfer toner particles to the photoconductor drum so that they adhere to the electrostatic image and can later be transferred to and fused with paper.
In magnetic brush development, a cylinder which may be magnetic is rotated in close proximity to the photoconductor. A portion of the cylinder passes through a reservoir containing magnetic developer material. As a result, this material is attracted to the cylinder and rotates with it in the form of a brush or a tuft of material that is pulled across the photoconductor surface. Originally, the developer was a two component material in which toner was mixed with a magnetic carrier material. However, in recent years, attempts have also been made to produce a one-component developer material wherein the toner has magnetic properties.
When toner is used with carrier material, the developer is tumbled in the reservoir. As a result, the toner develops triboelectric charge and is attracted to the carrier. The toner and carrier are then carried against the photoconductor drum and tumble along the surface so that the toner particles are attracted to the charged image on the photoconductor and stick to it, as opposed to staying with the carrier. The carrier particles continue to be attracted to the cylinder and are returned to the reservoir.
It is well known that when round or shot carrier is used in a developer mix, the final image has good line definition but it does not fill large areas very well. Examples of this type of carrier are described in U.S. Pat. No. 4,331,757 of Tanaka, et al.
It is also known in the art to use flake or irregular carrier. See for example U.S. Pat. No. 3,278,439 of Blanchette. With such carrier, there is better image fill because it creates hot spots, but edge definition is not very good. Attempts have been made to improve developer performance with very irregular shapes for shot carrier, for example, a sponge-like shot carrier.
U.S. Pat. No. 2,965,573 of Gundlach suggests a combination of spherical carriers and cylindrical non-magnetic and electrically conductive filaments. Such a developer mix, while useful in cascade development systems, is not useful in magnetic brush development. The non-magnetic property would inhibit the formation of the chains of carrier particles that create the magnetic brush and the conductive property may tend to short out the magnetic cylinder. Consequently, the various shortcomings of the available developer materials have not been entirely overcome.